Penzey's should have celery salt. You might try the Italian grocery on Scottsdale road for the sport peppers and relish. I don't remember seeing them there, but they had proper Chicago giadinara so who knows?
I think I got my celery salt in the regular supermarket. People always give me strange looks when I put it on my hot dogs. Not sure why, since it appears to be popular in Chicago. All the little places we went to in Maine growing up had it as an option.